Fix error when assigning NaN to an integer column

Also covers any non-castable case by returning nil, which
is in-line with the intention of the former implementation,
but covers the odd cases which respond to to_i but raise
an error when it's called, such as NaN, Infinity and -Infinity.

Fixes #8757
Merge pull request #8781 from trisweb/tristan_8757_integer_column_nan_error_fix

Fix error raised when assigning NaN to an integer column